1. Field of the Disclosure
The following is directed to composite articles, and particularly, composite articles comprising reaction bonded silicon carbide bodies.
2. Description of the Related Art
Various composite materials are commercially available, including certain ceramic composite bodies incorporating silicon carbide. Silicon carbide-based ceramic materials have been utilized in many applications for their refractory properties and mechanical properties. Among the types of silicon carbide-based ceramics available, various types exist based on the particular forming process, including for example, sintered silicon carbide, hot pressed silicon carbide, and recrystallized silicon carbide. Each of the various types of silicon carbide bodies can have distinct features. For example, sintered silicon carbide (such as Hexoloy®) can be a very dense material, but is generally expensive and complex to produce. On the other hand, more cost effective but relatively porous silicon carbide materials such as nitride-bonded silicon carbide (known by acronyms such as NBSC and NSIC) have found practical use in refractory applications. Such refractory components include furnace or kiln furniture utilized in connection with holding or supporting work pieces during firing operations, as well as refractory lining materials.
Nitride-bonded silicon carbide tends to be a comparatively porous material, oftentimes having a porosity within a range of about 10 to about 15 vol %. These components are manufactured from a green body containing silicon carbide and silicon, and sintering the green body in a nitrogen containing atmosphere at temperatures on the order of 1,500° C. While nitride-bonded silicon carbide has desirable high temperature properties, it unfortunately suffers from poor oxidation resistance when used in oxidizing conditions, due in part to its intrinsic porosity. This particular characteristic has been addressed in the past by re-firing nitride-bonded silicon carbide components in an oxidizing atmosphere to form a thin oxide layer of amorphous or glassy silica, which functions to passivate and seal the outer surface of the component. Other techniques have focused on forming an outer, protective layer by firing a glass former, such as a silica-containing coating or a silica precursor, which is coated on the component. However, unfortunately, such processing pathways tend to form porous layers that have a propensity to crack and spall during use, rendering the outer protective layer of limited effectiveness.
In view of the state of the art of silicon carbide-based materials, there is a need in the art for improved composites.